The present invention relates to a method and device for operating a dispersed (distributed) control system in a vehicle.
In motor vehicles, dispersed control systems are used currently, or will be in the future, in many application cases, provision being made in control systems of this type for decentralized electronics, which drive control elements xe2x80x9con-site,xe2x80x9d optionally in cooperation with central control electronics. Systems of this type are provided above all for controlling braking systems, whether in the case of electro-pneumatic, electro-hydraulic braking systems or braking systems having an electromotive clamping of the wheel brakes. In addition, dispersed systems of this type can also be employed in internal combustion engine control, for example for controlling a throttle valve, or for steering controls.
German Patent No. 196 34 567 concerns a dispersed control system of this type. As discussed, a braking system is shown that has wheel brakes having electromotive clamping. For making available the desired quantities for the individual wheel brakes, at least one central electronics is provided that, via at least one communications system, provides the quantities or values, which may be necessary for controlling the wheel brakes, to control units that are arranged xe2x80x9con-sitexe2x80x9d with respect to the wheel brakes. Via the communications system, the central unit receives the operating quantities necessary for controlling the wheel brakes, the operating quantities being determined onsite by the individual wheel control units. For assuring operating safety, provision is made for two power sources (batteries, vehicle electrical systems), that are independent of each other, for supplying the individual electrical elements. Accordingly, the individual electrical elements are supplied either by the two sources or by one of the sources, so that if one of the sources fails, at least partial operation of the braking system can be maintained. For communicating between the central control units and the control units disposed xe2x80x9con-sitexe2x80x9d for controlling the wheel brakes, provision is made for two communications systems (bus systems), that are physically and/or electrically separated from each other. Since these bus systems are also supplied by different power sources, even in the event of the failure of one power source or of one communications system, at least partial operation of the braking system continues to be possible.
For example, the publication xe2x80x9cVDI Reports No. 1415, 1998, pp. 325 through 344xe2x80x9d concerns an electrical braking system that uses an error-tolerant, timed communications system (which may be referred to as a TTP/C communications system). In this dispersed braking system, the individual electronic units are connected to each other by a bus system, the communication being carried out in accordance with a timed protocol, such as the TTP/C protocol. In this context, as concerns hardware, the bus system is composed of two bus systems that are redundant with respect to each other, resulting in two communications channels, to which all electronic systems of the distributed or dispersed control system have access. It is precisely in the case of applications that are critical to safety, in particular in the operation of a braking system, that at least partial functionality of the braking system control is necessary even in the event of the failure of a power source. This also applies when a redundant communications system of this type having a timed protocol is used.
It is an object of an exemplary embodiment of the present invention, specifically in connection with a safety-critical, dispersed vehicle control system, to fulfill the requirements having to do with power supply, even when a timed-redundant bus system is used.
The requirements with respect to the power supply of a communications system used in safety relevant, dispersed control systems in vehicles, in particular in braking systems, are met even when, as a communications system, an error-tolerant bus system having at least two independent communications channels (e.g., having a TTP/C protocol) is used. In a particularly advantageous manner, in the event of the failure of a power source, the normal operation of at least one part of the communications system and therefore also of the control system is assured.
In an exemplary embodiment of the present invention, the communications channels of the bus, whose hardware is configured so as to be redundant, are each supplied by completely independent (i.e., physically separated power sources) and are themselves not electrically coupled. Thus the effects of a fault, such as a short-circuit in an energy storage mechanism or an earth short-circuit of the bus channel, on the respective power circuit remain limited and the overall system remains partially functional.
It is believed that the corresponding advantages are achieved not only in connection with the use of a TTP/C bus, but also with the use of any suitably appropriate bus system having redundant communications channels, especially having a timed protocol.
In an exemplary embodiment of the present invention, redundancy is assured both with respect to the physical transmission as well as with respect to the voltage supply of the bus. This improves the availability and the operational safety of the control system significantly.
In an exemplary embodiment of the present invention, the electrical separation is achieved using optical elements.
In an exemplary embodiment of the present invention, redundancy with respect to the power supply of the bus is realized through the fact that the bus driver microchips of an electronic system connected to the bus are supplied by different power sources for each channel, whereas the actual controller microchip, which is present for each system only singly for both channels, is connected for bus access to only one power source. In this manner, in the event of the failure of one power source, it remains possible for at least parts of the dispersed system to communicate via the still functional channel.